1. Field of the Invention
The present invention relates to a remote copy control method, and more particularly, to a remote copy function which duplicates data between disk subsystems not via a host computer. Further particularly, the present invention relates to a definition and control method for a command transmitting route of a disk controller (DKC) without a direct path from the host computer in the remote copy between the disk controllers arranged on three or more sites.
2. Description of the Prior Arts
A remote copy technology is known to hold the copy of a volume of a disk subsystem in a disk controller which is remotely arranged and to synchronously or asynchronously transmit updated data, for the purpose of saving, from any accidents, data stored in the volume.
For example, Japanese Unexamined Patent Publication No. 2003-122509 and Indication of Existence of Patent No. 2002-542526 disclose a method for maintaining the data copy by cascade-connecting three disk controllers in order to reduce the risk upon accidents and to suppress the bandwidth necessary for a network. The disk controllers do not necessarily have the host computer and, it is advantageous in term of the reliability to execute the remote copy or state acquisition via a communication line between the disk controllers, as compared with such a case via the host computer having a possibility of a network default and a host computer default. Consequently, according to a multi-hop method disclosed in Japanese Unexamined Patent Publication No. 2003-122509 and Indication of Existence of Patent No. 2002-542526, the updated data is transmitted from the host computer via the communication line between the disk controllers.
Further, according to the abovementioned related arts, in order to issue a remote command for remote copy control serving as a command for the disk controller describing remote copy operation contents for a volume pair, which is transmitted from the host computer via another disk controller, it is necessary to describe a multi-hop list serving as a route to an operand of a host command. Therefore, in the case of changing the connection structure between the disk controllers or between the disk controller and the host computer, all the files describing the host command need to be changed. Further, in the case of describing the processing for executing the command from a remote site for recovery, it is necessary to obtain a route from the host computer on the recovery site and describe the multi-hop list. When the command can be inputted from a plurality of routes, the command is inputted via another route after causing a link default by describing the host command describing the other route.